1. Field of the Invention
The present invention relates to a spin-valve type thin film element in which electrical resistance changes in response to the relationship between the magnetization direction of a fixed or pinned magnetic layer and the magnetization direction of a free magnetic layer which is influenced by an external magnetic field. More particularly, the invention relates to a spin-valve type thin film element in which the magnetization of a fixed magnetic layer can be properly fixed in the height direction and to a method of manufacturing such a spin-valve type thin film element.
2. Description of the Related Art
FIG. 7 is a sectional view of a spin-valve type thin film element (spin-valve type thin film magnetic head), taken near the air bearing surface (ABS), which detects a recording magnetic field from a recording medium such as a hard disk. FIG. 8 is a perspective view which schematically shows the entire structure of a thin-film magnetic head provided on a slider.
A spin-valve type thin film element 1 shown in FIG. 7 is a kind of giant magnetoresistive (GMR) element which uses a giant magnetoresistance effect, and is used for detecting a recording magnetic field from a recording medium such as a hard disk.
As shown in FIG. 7, in the spin-valve type thin film element 1, a free magnetic layer 5, a nonmagnetic conductive layer 4, a fixed magnetic layer 3, and an antiferromagnetic layer 20 are deposited in that order, and hard magnetic bias layers 6 and 6 are formed on both sides thereof.
Generally, an iron--manganese (Fe--Mn) alloy film or iridium--manganese (Ir--Mn) alloy film is used for the antiferromagnetic layer 20, a nickel--iron (Ni--Fe) alloy film is used for the fixed magnetic layer 3 and the free magnetic layer 5, a copper (Cu) film is used for the nonmagnetic conductive layer 4, and a cobalt--platinum (Co--Pt) alloy film is used for the hard magnetic bias layers 6 and 6. Numerals 7 and 8 represent an under layer and a protective layer, respectively, composed of a nonmagnetic material such as tantalum (Ta).
As shown in FIG. 7, the fixed magnetic layer 3 and antiferromagnetic layer 20 are formed so as to be in contact with each other. By depositing films in a magnetic field, an exchange anisotropic magnetic field is caused by exchange coupling at the interface between the fixed magnetic layer 3 and the antiferromagnetic layer 20, and thus the fixed magnetic layer 3 is put into a single magnetic domain state and the magnetization direction of the fixed magnetic layer 3 is fixed in the Y direction (height direction; the direction of a leakage magnetic field from a recording medium).
After depositing six layers from the under layer 7 to the protective layer 8 (hereinafter referred to as a "laminate"), both sides of the laminate are scraped off so that the laminate has inclined sides by an etching process such as by ion-milling, and hard magnetic bias layers 6 and 6 are deposited on both sides. The hard magnetic bias layers 6 and 6 are magnetized in the X direction (track width direction).
The magnetization direction of the free magnetic layer 5 is set in the X direction under the influence of the hard magnetic bias layers 6 and 6 which are magnetized in the X direction.
In the spin-valve type thin film element 1, a sensing current is applied from conductive layers 9 and 9 formed on the hard magnetic bias layers 6 and 6 into the fixed magnetic layer 3, nonmagnetic conductive layer 4, and the free magnetic layer 5. The driving direction of a recording medium such as a hard disk is in the Z direction, and if a leakage magnetic field from the recording medium is applied in the Y direction, the magnetization of the free magnetic layer 5 changes from the X direction to the Y direction. Because of the relationship between the change in the magnetization direction in the free magnetic layer 5 and the fixed magnetization direction of the fixed magnetic layer 3, the electrical resistance changes, and the leakage magnetic field from the recording medium is detected by the voltage change based on the change in the electrical resistance.
As shown in FIG. 8, the spin-valve type thin film element 1 is formed on a magnetic lower shield layer 12 formed on an end 11a on the trailing side of a slider 11 with a nonmagnetic lower gap layer (not shown in the drawing) therebetween.
A magnetic upper shield layer 13 is formed on the spin-valve type thin film element 1 with an upper gap layer (not shown in the drawing) therebetween. The layers from the lower shield layer 12 to the upper shield layer 13 function as a reading head h1.
The upper shield layer 13 also functions as a lower core layer for an inductive type magnetic head h2 (for writing).
In the inductive type magnetic head h2, as shown in FIG. 9, a gap layer 14 composed of a nonmagnetic material such as aluminum oxide (Al.sub.2 O.sub.3) is provided on the lower core layer 13, and a resist layer 15 is formed on the gap layer 14.
A coil layer 16 spirally formed (refer to FIG. 8) is provided on the resist layer 15, and a resist layer 17 is formed on the coil layer 16.
An upper core layer 18 is formed by plating a magnetic material such as a permalloy on the resist layer 17.
In the inductive type magnetic head h2, a recording current is applied into the coil layer 16, and a recording magnetic field is applied onto the upper core layer 18 and the lower core layer 13 from the coil layer 16. A leakage magnetic field between the lower core layer 13 and the upper core layer 18 at a magnetic gap G section enables magnetic signals to be written into a recording medium such as a hard disk.
As described above, after the laminate including the free magnetic layer 5, the nonmagnetic conductive layer 4, the fixed magnetic layer 3, and the antiferromagnetic layer 20 is formed, that is, the antiferromagnetic layer 20 is deposited in a magnetic field to generate an exchange anisotropic magnetic field, hard magnetic bias layers 6 and 6 are formed on both sides of the laminate, and then the hard magnetic bias layers 6 and 6 are magnetized in the X direction (track width direction).
Next, the inductive type magnetic head h2 shown in FIG. 9 is formed on the spin-valve type thin film element 1.
In the fabrication process of the inductive type magnetic head h2, in order to increase insulating properties of the resist layers 15 and 17 shown in FIG. 9, after forming the resist layers 15 and 17, the resist layers 15 and 17 must be heat-treated for curing.
However, if the resist layers 15 and 17 are heat-treated for curing, the magnetization of the fixed magnetic layer 3 that has been fixed in the Y direction in FIG. 7 fluctuates in the X direction, and playback characteristics of the spin-valve type thin film element 1 deteriorate.
The problem described above results from the relationship between the blocking temperature of an antiferromagnetic material used as the antiferromagnetic layer 20 and the heating temperature for curing the resist layers, and the magnetization direction of the hard magnetic bias layer 6.
The conventional antiferromagnetic layer 20 is composed of an Fe--Mn alloy film or an Ir--Mn alloy film. The Fe--Mn alloy layer has a blocking temperature (temperature at which an exchange anisotropic magnetic field disappears) of approximately 150.degree. C. and the Ir--Mn alloy film has a blocking temperature of approximately 260.degree. C.
FIGS. 10A and 10B are schematic diagrams which show the fixed magnetic layer 3 and the hard magnetic bias layer 6 viewed from directly above. FIG. 10A shows the magnetization directions of the fixed magnetic layer 3 and the hard magnetic bias layer 6 before the resist curing step, and FIG. 10B shows the magnetization directions of the fixed magnetic layer 3 and the hard magnetic bias layer 6 after the resist curing step.
As shown in FIG. 10A, before the resist curing step (before heat-treatment), a magnetization B in the central region of the fixed magnetic layer 3, is fixed in the Y direction (height direction) by an exchange anisotropic magnetic field in the Y direction caused in the interface with the antiferromagnetic layer 20.
However, a magnetization C in the end regions of the fixed magnetic layer 3 is easily influenced by a magnetization A in the X direction (track width direction) of the adjacent hard magnetic bias layer 6, and thus the magnetization C is fixed in the direction inclined in the X direction in relation to the Y direction.
In the state of magnetization shown in FIG. 10A, heat-treatment is performed for curing the resist layers at approximately 250.degree. C. When the antiferromagnetic layer 20 (refer to FIG. 7) is formed of an Fe--Mn alloy film, the heating temperature is higher than the blocking temperature (approximately 150.degree. C.) of the Fe--Mn alloy film, or when the antiferromagnetic layer 20 is formed of an Ir--Mn alloy film, the heating temperature is substantially the same as the blocking temperature (approximately 260.degree. C.) of the Ir--Mn alloy film.
However, when heat-treatment is performed at approximately 250.degree. C. for curing the resist layers 15 and 17, the exchange anisotropic magnetic field in the Y direction disappears, and thus the fixed magnetic layer 3 is strongly influenced by the hard magnetic bias layer 6 that is magnetized in the X direction.
Therefore, when the temperature is decreased to ambient temperature and an exchange magnetic coupling is regenerated at the interface between the fixed magnetic layer 3 and the antiferromagnetic layer 20, the anisotropy disperses, and as shown in FIG. 10B, magnetizations C' and C' in the end regions of the fixed magnetic layer 3 that are strongly influenced by the hard magnetic bias layer 6 are fixed in the X direction, and also, the magnetization B' in the central region of the fixed magnetic layer 3 is fixed in the direction inclined to the X direction in relation to the Y direction.
As described above, the magnetization of the fixed magnetic layer 3 of the spin-valve type thin film element 1 is not properly fixed in the Y direction in the entire region, and thus playback characteristics deteriorates, for example, the output of the head decreases, or satisfactory asymmetry cannot be obtained. The word "asymmetry" means the vertical asymmetry of the regenerated output waveform.